Previous studies have shown the occurrence of short-duration plasma flow bursts, typically lasting a few minutes, within the cusp region, often accompanied by the poleward motion of the 630-nm aurora. In this study, we investigated the ion heating characteristics associated with a large-scale plasma flow burst, which coincides with a poleward expansion of the 630-nm aurora. We analyzed data from simultaneous observations using an all-sky imager at Svalbard, the EISCAT Svalbard Radar (ESR), and the SuperDARN radar at Hankasalmi. Additionally, we examined magnetic perturbation data from the Swarm satellites as complementary data to assess the presence of a significant east–west component in the plasma flow. The plasma flow burst was detected by the ESR at approximately 10:40 UT on 8 December 2016, indicated by an increase in the F-region ion temperature (<InlineEquation ID="IEq1"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="40623_2025_2264_Article_IEq1.gif" Format="GIF" Height="16" Rendition="HTML" Resolution="72" Type="Linedraw" Width="18" /> </InlineMediaObject> <EquationSource Format="TEX">${T}_{i}$</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>T</mi> <mi>i</mi> </msub> </math></EquationSource> </InlineEquation>) due to frictional heating arising from ion–neutral velocity differences. Coinciding with the arrival of the front of the plasma flow burst within the ESR’s field of view (accurate to within 1 min), the poleward boundary of the cusp electron precipitation, as observed in the 630-nm aurora, passed through the ESR’s field of view by moving poleward, seemingly drawn by the front of the plasma flow burst. The altitude profiles of <InlineEquation ID="IEq2"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="40623_2025_2264_Article_IEq1.gif" Format="GIF" Height="16" Rendition="HTML" Resolution="72" Type="Linedraw" Width="18" /> </InlineMediaObject> <EquationSource Format="TEX">${T}_{i}$</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>T</mi> <mi>i</mi> </msub> </math></EquationSource> </InlineEquation> revealed a local maximum at an altitude of approximately 150 km, where the temperature increased from ~ 1200 to ~ 1880 K within 4 min. At altitudes between 190 and 300 km <InlineEquation ID="IEq3"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="40623_2025_2264_Article_IEq1.gif" Format="GIF" Height="16" Rendition="HTML" Resolution="72" Type="Linedraw" Width="18" /> </InlineMediaObject> <EquationSource Format="TEX">${T}_{i}$</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>T</mi> <mi>i</mi> </msub> </math></EquationSource> </InlineEquation> was lower than this local maximum <InlineEquation ID="IEq4"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="40623_2025_2264_Article_IEq1.gif" Format="GIF" Height="16" Rendition="HTML" Resolution="72" Type="Linedraw" Width="18" /> </InlineMediaObject> <EquationSource Format="TEX">${T}_{i}$</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>T</mi> <mi>i</mi> </msub> </math></EquationSource> </InlineEquation> prior to the plasma flow burst, but rapidly increased to approximately match the local maximum <InlineEquation ID="IEq5"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="40623_2025_2264_Article_IEq1.gif" Format="GIF" Height="16" Rendition="HTML" Resolution="72" Type="Linedraw" Width="18" /> </InlineMediaObject> <EquationSource Format="TEX">${T}_{i}$</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>T</mi> <mi>i</mi> </msub> </math></EquationSource> </InlineEquation>. However, following this rapid increase, the <InlineEquation ID="IEq6"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="40623_2025_2264_Article_IEq1.gif" Format="GIF" Height="16" Rendition="HTML" Resolution="72" Type="Linedraw" Width="18" /> </InlineMediaObject> <EquationSource Format="TEX">${T}_{i}$</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>T</mi> <mi>i</mi> </msub> </math></EquationSource> </InlineEquation> enhancement at these altitudes appeared to be suppressed, with the estimated rate of suppression being −80 and −220 K/min. Based on the investigation through two-dimensional simplified numerical simulations, we suggest that the suppression of <InlineEquation ID="IEq7"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="40623_2025_2264_Article_IEq1.gif" Format="GIF" Height="16" Rendition="HTML" Resolution="72" Type="Linedraw" Width="18" /> </InlineMediaObject> <EquationSource Format="TEX">${T}_{i}$</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>T</mi> <mi>i</mi> </msub> </math></EquationSource> </InlineEquation> is likely due to the formation of a relatively fast neutral flow, driven by increased ion drag associated with ionization enhancement resulting from low-energy electron precipitation. Graphical Abstract

Suppression of ion heating in the cusp during plasma flow burst

期刊论文
出版模式：

开放获取
发表日期：

2025年8月18日

查看全文

Satoshi Taguchi,
Tomokazu Oigawa,
Yunosuke Nagafusa,
Hiroyuki Shinagawa,
Keisuke Hosokawa,
Yasunobu Ogawa,
Haruto Koike

摘要

Previous studies have shown the occurrence of short-duration plasma flow bursts, typically lasting a few minutes, within the cusp region, often accompanied by the poleward motion of the 630-nm aurora. In this study, we investigated the ion heating characteristics associated with a large-scale plasma flow burst, which coincides with a poleward expansion of the 630-nm aurora. We analyzed data from simultaneous observations using an all-sky imager at Svalbard, the EISCAT Svalbard Radar (ESR), and the SuperDARN radar at Hankasalmi. Additionally, we examined magnetic perturbation data from the Swarm satellites as complementary data to assess the presence of a significant east–west component in the plasma flow. The plasma flow burst was detected by the ESR at approximately 10:40 UT on 8 December 2016, indicated by an increase in the F-region ion temperature ( ${T}_{i}$ $T_{i}$ ) due to frictional heating arising from ion–neutral velocity differences. Coinciding with the arrival of the front of the plasma flow burst within the ESR’s field of view (accurate to within 1 min), the poleward boundary of the cusp electron precipitation, as observed in the 630-nm aurora, passed through the ESR’s field of view by moving poleward, seemingly drawn by the front of the plasma flow burst. The altitude profiles of ${T}_{i}$ $T_{i}$ revealed a local maximum at an altitude of approximately 150 km, where the temperature increased from ~ 1200 to ~ 1880 K within 4 min. At altitudes between 190 and 300 km ${T}_{i}$ $T_{i}$ was lower than this local maximum ${T}_{i}$ $T_{i}$ prior to the plasma flow burst, but rapidly increased to approximately match the local maximum ${T}_{i}$ $T_{i}$ . However, following this rapid increase, the ${T}_{i}$ $T_{i}$ enhancement at these altitudes appeared to be suppressed, with the estimated rate of suppression being −80 and −220 K/min. Based on the investigation through two-dimensional simplified numerical simulations, we suggest that the suppression of ${T}_{i}$ $T_{i}$ is likely due to the formation of a relatively fast neutral flow, driven by increased ion drag associated with ionization enhancement resulting from low-energy electron precipitation.

Graphical Abstract